How to Prep Weathered Wood for Painting

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Those of us with old, weathered outbuildings eventually reach a point where we must decide if a building is worth saving. Even though the structure might not have historic or architectural value, it may still be of use as a place to store garden equipment, keep chickens or house our collection of cars or auto parts.

Restoring an old, weathered outbuilding takes a little more work than you might expect. It may require being pulled "back into square" to reverse a noticeable racking. It may also need a new foundation, roof or cross braces for added support. But once the structural work is complete and the roof replaced, the last step of the restoration should be a coat of paint, a project that is also a little more work that you might expect.

Unpainted wood is said to have "weathered" which is usually characterized by a gray, washed-out appearance. Outbuildings that have stood for many years without paint may have areas of rot or have splintered or cracked in spots. Before weathered wood can be painted, it will require extensive prep work to ensure that the paint stays on for more than just a couple of years.

Step 1: Prepare the Surface

With old buildings such as my 130-year-old barn, water-blasting the loose paint is not a recommended practice. The high pressure of the sprayer can knock those old boards loose and infuse the bare areas of wood with water. Instead, the paint should be scraped off by hand using a paint scraping tool. Do keep in mind that old paint may contain lead, and proper precautions should be taken when removing those old fragments of paint.

As you scrape away the paint, this is the time to take note of the wood's condition. Old, weathered wood that is moist and spongy is said to suffer from "damp" or "wet" rot. Areas that are dry and crumbly are referred to as "dry rot." Both dry and damp rot are caused by microorganisms that must be removed to prevent the rot from spreading. For smaller areas of rot, cutting away the damaged section and patching it with a wood plug will do. Larger areas of damage may require replacing whole sections of lap siding, which can be milled at a custom millworks company.

Other damage to look for during the scraping process are warped or twisted planks or extensive cracks in the wood which typically occurs in desert climates. These sections of wood should also be replaced.

Step 2: Sand and Brush

Once wood has been scraped and the damaged sections replaced, it's time to grab a wire brush and sander for the next leg of the project.

Wood that has been exposed to weather will eventually break down into a matte of dense fibers that can be scraped loose with a fingernail. Before you can cover up that weathered wood with a coat of paint, those loose fibers must be removed. For larger structures, a wire brush is an easy way to knock off the remaining pieces of paint and surface fibers, while also roughing up the wood's surface for better paint adhesion. Flat surfaces such as moldings and soffits can be easily sanded with a belt sander.

While you might not want to put this degree of work into prepping your old outbuilding or barn, this is an important step that will ensure a long-lasting paint job and the future longevity of the structure.

Step 3: Apply Caulk Where Needed

Even an old outbuilding can benefit from a little caulking. Caulk prevents water from seeping behind vulnerable areas of the outbuilding and developing into rot.

We used a high-quality acrylic caulk on our barn to seal the corner joints, seams and trim pieces around doors and windows. The caulk not only protects the wood, but gives a nice clean look to the architectural details of the structure by removing shadow lines.

Step 4: Wash It Down With a Hose

Once the caulk has dried, the outbuilding can be given a good rinsing with a garden hose and scrub brush to knock off dirt, sawdust and other debris that may prevent paint from properly adhering. After washing, the building should be allowed to dry thoroughly.

For taller buildings, we discovered an RV cleaning brush extended our reach by about six feet and was a real time-saving tool for scrubbing down our two-story barn. This hollow, long-handled brush attached to a garden hose, and allowed us to rinse and scrub the barn all in one step. These brushes are available at RV centers and cost around $80.

Step 5: Apply Primer

The saying goes that a "paint job is only as good as the primer." While it may be tempting to slap some paint on the outbuilding and call it good, for a more attractive and long-lasting paint job, applying a primer base coat is an important step that should not be skipped. Primers help to block stains that can seep into your topcoat, provides a clean and uniform finish and will improve topcoat adhesion. Without a primer, the top coat is more susceptible to flaking.

Since our barn had been treated with linseed oil in the past, it was recommended that we use a high-quality, oil-based primer, applied in two separate applications at a 24-hour interval. The first application of primer was absorbed immediately into the wood, but the second application of primer did a fantastic job of covering the weathered siding. The two applications of primer were followed with two coats of high-quality exterior latex paint for a clean, smooth finish. Had the barn not been treated with linseed oil, a high-quality latex primer could have been used instead.

Painting an old, weathered building is not an easy overnight task for the do-it-yourselfer and can take several weeks to get it just right. But for an old-house person who loves the look of a historic outbuilding on their property, restoring a weathered old barn is a project most certainly worth doing.